1. Field of the Invention
This invention relates to a control system for internal combustion engines for vehicles, and particularly to a control system for an automotive internal combustion engine which is equipped with a so-called DBW (Drive By Wire) system, which electrically controls the opening of a throttle valve of the engine according to an operating amount of an accelerator pedal of the vehicle.
2. Prior Art
A control system for internal combustion engines for vehicles is known, for example, from Japanese Laid-Open Patent Publication (Kokai) No. 53-40128, which is intended to prevent deterioration and capacity loss of a catalytic converter of the engine during the operation of the engine in a high rotational speed and high load condition, and controls the air-fuel ratio of an air-fuel mixture supplied to the engine to a richer side than a stoichiometric air-fuel ratio to effect cooling by fuel to thereby control the temperature of the catalytic converter to a value lower than a predetermined value, when the engine is operating in such a high rotational speed and high load condition.
However, according to the known control system, the air fuel ratio of the air-fuel mixture deviates to the richer side than the stoichiometric air-fuel ratio, and as a result, the purification ratio of the catalytic converter can be degraded, so that exhaust gases with increased amounts of noxious components are emitted from the engine.
Further, according to the known control system, the amount of fuel is increased due to the enriching of the air-fuel ratio of the air-fuel mixture, which degrades the fuel economy.